1. Field of the Invention
The present invention pertains to an apparatus for growing crystals such as high purity silicon single-crystals.
2. Prior Art
In the manufacture of silicon single-crystals by Czochralski technique, the contact area between a silicon melt and a quartz crucible varies as the quantity of the melt decreases due to the pulling of the crystals, and hence the quantity of oxygen dissolved from the crucible varies. In recent years, however, severe standards have been adopted as to both oxygen and dopant concentrations of silicon single-crystals for use as substrates for semiconductor devices. For this reason, it has been only a part of the ingot that can be utilized as the semiconductor devices, deteriorating the yield of material.
Proposed in order to obviate the above problem is an apparatus of the type which keeps the quantity of the melt constant by continuously adding granulated silicon powder material to a crucible to compensate the amount of the pulled crystal (Examined Japanese Patent Application Publication No. 57-40119). In such apparatus, however, the surface of the melt is ruffled upon the falling of the material to develop a disturbance which is transmitted to the crystallization front of the single-crystal ingot, so that crystal defects such as dislocation are caused.
To cope with this problem, a cylindrical partition wall has been disposed between the single-crystal ingot and the portion into which the material falls U.S. Pat. No. 2,892,739 and Non-Examined Japanese Patent Application Nos. 57-183392 and 61-36197). However, there still remains a disturbance which is transmitted to the crystallization front through apertures formed to communicate the outer and inner sides of the partition wall. Besides, the provision of such partition wall requires the use of a crucible greater in size since the space between the partition wall and the crucible as well as the space between the crucible and the crystal ingot has to be rendered sufficiently large. As a result, a large quantity of silicon material is required to ensure a sufficient depth of the silicon melt, resulting in an increase of costs as compared with the apparatus without the partition wall. In addition, the above apparatuses have further disadvantages that the silicon crystals are liable to deposit on the surface of the partition wall, so that the conditions on crystal growth may vary. On a certain occasion, the growing of single-crystals may be even hindered.